Forgot to update Readonly `SpinBox`es to Qt 2 when implementing Cura
8684. As the spinbox is used in various places with the same
functionality it made sense to create a reusable component.
There is still a feature gap in the implementation; The `SpinBox`es
from QtControls 2.x value is defined as an integer. For some use-cases
we do require a fractional value in the `SpinBox`. The only two places
where this is required are the `material_diameter` and
`material_density` fields in the material prefference page.
Cura 8684
